Computer systems employ power management for several reasons. Laptop computers and other mobile computers typically employ power management to extend battery life. Desktop and larger computer systems employ power management to reduce energy costs and to promote energy conservation. Enterprise computer installations sometimes must employ power management to maintain power consumption within the limits imposed by electrical utilities and power delivery infrastructure. In addition, power management may be used to limit heat dissipation so that computers do not overheat or impose an undue burden on heat-removal facilities.
Power management can be automated or implemented manually. For example, power management can involve a user shutting down a computer during long periods of non-use, or a computer automatically shutting down or entering a low-power state after a predetermined period of inactivity. Some power management schemes involve both user input and automated activity. For example, a software shutdown proceeds through a series of steps to preserve data before cutting off power to computer components. For another example, the criteria according to which a computer shuts down or changes a low-power state are often user selectable.